Removing Hemco plenum..Am I crazy?

[brian]

That is exactly what I am trying to do...arrive at a more equal flow for tuning and high boost safety measures than the Hemco alone can achieve. I understand Brian's point about the Hemco but I would like to try some new technology and see if it makes a differnece. Thats all.

Ed,
Think of it as a 4BL manifold. The optimal design is to dump air into the center of the plenum. Perfect would be a pipe straight into the plenum, rather than a '90' as our upper plenums do. Unfortuanatly, due to underhood fitment issues this is not possible.
The Hemco drops the air directly into the center to be distributed equally.
The smaller opening does make one question the actual usefulness of this plenum. But, upon installation of every one I have installed fuel pressure had to be raised due to the motor running leaner. (more air)
Years ago Red Armstrong did not believe the worked either. Janes car was run at White Racing on their dyno fo actual testing. Needless to say, 40 hp on her car. That was around 620 at the wheels.

These plenums may look pecular, but the undoubtably work.
My original offer still stands though.

Ed, I am sure whatever you decide, will be best for your car`s combo.
The plates must work, as RJC sells a bunch of them. My experience goes back to installing my first one. I never looked back. Or around for that matter.

Brian

 

[87NAT]

Brian,

Would u take $30 off my next tranny? Because once I install that plate I might blow mine up with all the extra boost I can make... Seriously, thanks for your input and I will probably do a real world test when I am at the track and actually look at my A/F numbers and MPH. 15 minutes to swap plenums is worth it to me to see which one works better. I am sure other board members would be curiuos also.

 

[CTX-SLPR]

That is exactly what I am trying to do...arrive at a more equal flow for tuning and high boost safety measures than the Hemco alone can achieve. I understand Brian's point about the Hemco but I would like to try some new technology and see if it makes a differnece. Thats all.

Ed,
Think of it as a 4BL manifold. The optimal design is to dump air into the center of the plenum. Perfect would be a pipe straight into the plenum, rather than a '90' as our upper plenums do. Unfortuanatly, due to underhood fitment issues this is not possible.
The Hemco drops the air directly into the center to be distributed equally.
The smaller opening does make one question the actual usefulness of this plenum. But, upon installation of every one I have installed fuel pressure had to be raised due to the motor running leaner. (more air)
Years ago Red Armstrong did not believe the worked either. Janes car was run at White Racing on their dyno fo actual testing. Needless to say, 40 hp on her car. That was around 620 at the wheels.

These plenums may look pecular, but the undoubtably work.
My original offer still stands though.

Ed, I am sure whatever you decide, will be best for your car`s combo.
The plates must work, as RJC sells a bunch of them. My experience goes back to installing my first one. I never looked back. Or around for that matter.

Brian

Has anyone measures the output area of a Hemco? I'd be willing to bet the sqin of the hemco hole is smaller than the sqin of the RJC PP. My design qualm with the above example of a single plane is the fact that the lower plenum isn't square like a carbed intake and cramming the air into the middle of a rectangular box with suction points on the long sides means that the middle is more active and higher pressure than the ends which have semi stagnant air and lower pressure. This leads to inconsistancies and everyone who really tunes knows that you can only tune for the weakest link unless you have individual cylinder timing and injection controls. If your center cylinders are getting more air then you have a difference between them and the end ones. Throw in they are the most dangerous to tune because of the shared headbolts and thinnist gasket area between the bores and you can't get as agressive. In the FAST series of drag racing you can't modify the external carberator or external intake, lots of the guys run various dams, dividers, and plates in the plenums to try to tune the entire engine to run equally so you don't have a lean or a rich hole pulling the edgy tune down to keep it together. I'm sure the Hemco is effective, but I'm disputing it as the most effective solution.

 

[wyominggun]

KEEP the HEMCO. IF the idiot says its junk but wants to buy it off you dirt cheap then he sucks moose c@#k and is not a good member.

 

[87NAT]

KEEP the HEMCO. IF the idiot says its junk but wants to buy it off you dirt cheap then he sucks moose c@#k and is not a good member.

First of all Brian is not an idiot and he was making a joke. He had PM'd me about keeping the Hemco and I felt I was going to try the RJC anyway...he was being sarcastic. His knowledge and experience with these cars is invaluable and you dont have the right to call him out with your "30" posts and new member status. Do a search on Brians post's and you will see that he knows what hes talking about. Go to another board if you want to rag on one of our respected members. We dont need that here.

 

[wyominggun]

I will give you the best offer so far $35.00

 

[bison]

Can someone post up Bamford's egt tests with and without powerplates and any added plenum volume he used? The sq in opening on the plate is more than enough to cover a 62 mm tb inlet of 14.69 inches squared. Id bet it will outflow the 70 mm throttle body also. Another thing that helps in distribution especially at higher rpm's is a larger plenum volume. It slows the air down so it can be distributed more evenly without robbing the air from one cylinder to feed another as the intake valves open. There is more than just air in the intake at high rpm's anyway. There is actually a fog of fuel vapor the so the added volume does more than just help distribute the air. Its actually an air fuel mixture in the lower intake. There is a lot more to this than what ive stated in a lot of applications. The valve overlap and overall exhaust pressures have an impact on the cylinder to cylinder distribution which can be variable at different rpms because of ambient temps and throttle angles.

 

[JoelGN]

87NAT, this is my experience with a Hemco. Blew the passenger HG to the outside on #4. Once the heads were removed, #3 on the driver's side was distorted and about to go. I believe this plenum distributes more to the middle two cylinders where the HG's are the weakest. Couple that with the center four headbolts having to pull double duty, i.e., clamp two cylinders whereas the front/rear four pull single duty. I had no KR and the car felt really good but that may have been because the middle two were running so lean and mean. Since, I installed the RJC Precision/PP combo and all is well with several 23# boost runs. I tried to sell the Hemco but nobody even made an offer. IMO go with the RJC PP if you're truly trying to, "...arrive at a more equal flow for tuning and high boost safety measure.."

 

[PaCemkr86]

put the Hemco on ebay and let us fight over it...:smile:

 

[brian]

wyominggun KEEP the HEMCO. IF the idiot says its junk but wants to buy it off you dirt cheap then he sucks moose c@#k and is not a good member.

You sir, are the idiot.

Some people have a small sense of humor. You have none.

Thanks for the kind words... Brian

 

[brian]

First of all Brian is not an idiot and he was making a joke. He had PM'd me about keeping the Hemco and I felt I was going to try the RJC anyway...he was being sarcastic. His knowledge and experience with these cars is invaluable and you dont have the right to call him out with your "30" posts and new member status. Do a search on Brians post's and you will see that he knows what hes talking about. Go to another board if you want to rag on one of our respected members. We dont need that here.

YEAH!
:tongue: :wink:

 

[PaCemkr86]

Brian if you get the Hemco can we share it? :biggrin:

 

[Sweet6]

My buddy just put on a Hemco over his stock one. The car basically ran the same. 11.60s with stock and 11.60s with the hemco under the same conditions and same 60'. Same MPH too.

 

[wyominggun]

If callmebrian is offering his good name, I will offer $50.00 tops. And I aint calling you Brian, I've got another name for you

 

[hemity]

Has anybody tried the old school stock plenum 1/2" spacer under the hemco?

 

[at7we2]

had a Hemco. noticeable improvement over the stock upper plenum on on a basically stock combo. ran it for a while, then the RJC PP came out - I got an itch to try something new, sold the Hemco and re-installed the stock upper plenum with a PP. Honestly, didn't notice any difference, better or worse. Having said that, I really wish I had kept the Hemco and at least done some back to back testing, but I didn't.

From a "theoretical" standpoint, there's only two methods to balance multiple streams of diverging fluids (in this case, air).

1. *Reduce* the restrictions along the path(s) with the least airflow until the air volumes are equal. (this is one of the goals of head and plenum porting, the other objective being increasing overall airflow of course).

2. *Increase* the restriction in the paths with excessive airflow until the air volumes are equal.

I believe both the Hemco and the RJC PP accomplish #2 by restricting air flow to the rear cylinders which typically get too much air with the stock plenum.

I would expect the PP to cause more turbulence in the airstream than the Hemco plenum, *however* I believe Jason did a lot of research and flowbench testing to come up with the odd looking design of the PP and it would not surprise me if it actually worked a little better because it's really more of a "tuned" balancing device. The Hemco works by restricting the airstream and directing it at the center of the lower plenum. This relies on the lower plenum to distribute the air evenly. RJC tuned each PP design to work with the flow characteristics of the stock lower intake and specific upper plenums. The Hemco doesn't take into account any flow variations which may be designed or manufactured into the stock lower plenum.

IMO, it's 6 of one and a half-dozen of another. I've only had stock to very mild setups so my theories may not apply to higher HP setups.

Rob

 

[ThatDamGoldCar]

Take off the choke plate...

 

[87NAT]

Here is a pic of the Hemco that I pulled off. At least I think thats what it is . The letters "H. C." are stamped on the side.It does not look like the one that RJC has on his website pics. This came with my car so I never had a chance to really look at it. There is just one small hole in the center. It seems that it is focusing all of the air right in the middle . To me the RJC plate is going to distribute the air ALOT better. I just put the stock plenum and RJC on, started it, but didnt drive it yet. I can tell right away my car idles better, I will road test it tomorrow and give my feedback.

 

[PaCemkr86]

yes thats a Hemco...

 

[87NAT]

Anyone else has an opinion on this plenum design?